I am planning to replace my front brake pads within a month. I was told that if my brake wear sensor trips, I will need to buy new sensors as they will get destroyed. So I am trying to save my brake wear sensors by replacing the front brake pads before the sensor actually trips. For that, I am looking for a very rough estimate on how many kilometers I can do before my front brakes wear out by 1mm (this is how much is left before sensor tripping). This is considering mix of city/highway non-aggressive, slow braker style driving.

The car make is a 14 ' Audi S4 (B8.5).

  • 1
    Without a citation I will say that 1mm will = a lot. Way more than a month of normal driving. Commented Mar 29, 2016 at 2:26
  • not really an answer, but brake pads aren't all that expensive. why not just replace them and not have to worry about it?
    – Leliel
    Commented Mar 29, 2016 at 2:54
  • Because I have to drive ~ 100km a day and brake pads take 5 weeks to come in.
    – eYe
    Commented Mar 29, 2016 at 3:41

2 Answers 2


Here's a rough approach that should work regardless of vehicle

You will need to know

  • the current brake pad thickness
  • the thickness of a brand new brake pad
  • how much mileage you've put on the car since the last brake pad change.

The formula

Mileage per mm = mileage since last brake change
               / ( brand new thickness - present thickness )

In essence, this formula assumes a linear wear rate.


New E39 M5 brake pad thickness = 10 mm
Old E39 M5 brake pad thickness = 2 mm
Mileage accrued                = 25,000 km

Mileage per mm = 25,000 km / ( 10 -2 ) mm
               = 3,125 km per mm

So I can now anticipate roughly when the next brake pad replacement is due before the brake wear sensor trips.

E39 M5 Brake Pads - new vs old

  • Side note: brake wear sensors are relatively inexpensive. Unless there is some untoward hassle involved in replacing them I wouldn't worry about having them trip.
    – Zaid
    Commented Mar 29, 2016 at 2:54
  • Well, I see them listed at $38 each for the cheapest ones :/
    – eYe
    Commented Mar 29, 2016 at 2:56
  • @eYe A bit much for what is essentially a loop of wire, I agree. I was more used to values in the sub-$15 range, but then again your car is still relatively new
    – Zaid
    Commented Mar 29, 2016 at 3:31
  • @Zaid Beauty answer. +1 Commented Mar 29, 2016 at 5:52

From what I can see, if you opt for the Pagid, Bosch, Brembo or ATE front pads for this vehicle, the wear sensor is included in the box. It is also available separately with a UK retail price of the equivalent of less than 20 USD.

Have you checked with the supplier of your new pads to establish if the sensor is included or not? Wear sensors are sacrificial components that are both cheap and easy to replace.

As for how long your pads will last before you trip the sensor, this is impossible to gauge. You may, driving gently and allowing the car to coast, get several months use. You may however find that a single piece of evasive action taken at highway speeds is enough to trip your sensor. The S4 is a fiercely quick car and relatively heavy too so it would be possible to burn up a brand new set of pads in a single afternoons track use.

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